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Formable paint films are new alternative for exterior finishing.

Exterior automotive thermoplastic parts can now be "painted" in the mold without the capital investment or environmental-compliance expenses of actual paint-finishing facilities. Using a paint-film technology developed by Avery Dennison's Automotive Div., Troy, Mich., molders can apply a durable exterior coating to injection molded parts via an insert-molding technique. The insert is a thermoformed shell made from a thin thermoplastic sheet already coated with a formable dry paint film. This technique reportedly provides a smooth, high-gloss painted surface that meets automotive requirements (see PT, June '92, p. 14).

The first commercial exterior application appears on the 1994 GMC Sonoma pickup truck, which has body-side moldings with a brushed-aluminum look. That look comes from the Avloy formable dry-paint finish supplied by Avery Dennison. Avloy proved to be the only technology available that could achieve the brushed-metal appearance without actually using a stamped or extruded metal component, according to Avery Dennison.

Product manager Cliff Nastas says Avery Dennison is working on other exterior automotive applications. He reveals, for example, that the Avloy technology will be used on mirror housings for 1995 Ford vehicles, and that its use on window pillars is currently being explored. "We have several projects under way, including more body-side moldings, automotive fascias, pillars, spoilers, and mirror housings. We're looking into almost every paintable exterior part on a vehicle."

The company has had an indoor version of the Avloy technology, called Thermark, for over 15 years. That insert-molding technique has been used on auto interior trim such as dashboards. These interior applications have been chiefly simulated wood-grain finishes.

DRY-FILM ADVANTAGES

Avloy allows molders to apply a base coat and clear-coat finish simultaneously during the molding process, without secondary operations and without the volatile organic compound (VOC) emissions generated by spray painting. Paint-sludge disposal is likewise eliminated. In addition, there is no difficulty making color changes--and no downtime either.

The base coat and clear coat are both acrylic polyvinylidene difluoride (PVDF) formulations. Because PVDF is a very inert and very uv-stable polymer, it has excellent chemical resistance to industrial air pollution, unlike spray-applied base-coat/clear-coat systems.

These characteristics reportedly translate into improved gloss retention and excellent weatherability. After three years of outdoor exposure in Florida, parts made with Avloy retained 85-90% of original gloss--versus only 50-60% retention with conventional base-coat/clear-coat paint systems--whether on metal or plastic exterior parts, explains Nastas. Also, Avloy laminates can provide extremely smooth finishes free of "orange peel" and can hide the presence of fillers in molding resins. They also can hide the use of regrind from recycled plastics.

Besides eliminating the capital expenditures required for paint shops, the dry-film process allows molders to use lower-cost, less heat- and solvent-resistant plastics. In addition, notes Nastas, "Some molders have tended to use ABS in place of TPO or PP because of paintability problems associated with polyolefin-based materials. With the dry paint film, you eliminate the problem of poor paint adhesion."

Besides supplying Avloy in high-gloss, low-gloss, metallic, and solid colors, Avery Dennison also can introduce printed patterns or designs between the base coat and clear coal. For example the Sonoma body molding has been given a brushed-aluminum look by applying a high-definition gravure-printed brush pattern between the two. "This allows you to achieve a look that simply cannot be done with spray painting," says Nastas.

Moreover, the paintable film is "very cost-competitive" with spray painting, based on several studies with molders and automotive OEMs, according to Nastas. "In most instances, Avloy proves to be less expensive."

HOW IT'S DONE

Avloy is made by casting wet paint films--first a clear coat and then a base coat--onto a PET film carrier by reverse roll coating. On top of the base coat goes a layer of thermoplastic adhesive. Next, the cured paint-film layers are laminated to a thermoplastic backing sheet by means of heat and pressure, after which the original carrier web is stripped away. The 0.02-in. plastic backing sheet can be of various resins, such as ABS, TPO, PET or polycarbonate.

The dry paint-film laminate (supplied in roll form) is thermoformed and precision trimmed into the shape of the finished part. This preform is then inserted into the injection mold cavity. The mold is injected with the same material as the backing sheet, causing a melt bond to form that results in the dry-film laminate becoming permanently integrated into the final part.

Textured finishes can be embossed onto the dry paint film by applying the appropriate texture to the cavity side of the mold. For unique design effects, pressure-sensitive graphics can be applied directly to the preform prior to injection molding. The high pressure and temperatures of injection molding force the graphic into the paint-film surface, leaving a "zero-profile" appearance.

PRESSURE-SENSITIVE 'PAINT'

Another newly commercial dry-film product from Avery Dennison has been applied on the "B" pillars of the extended cabs of the 1994 GMC Sonoma and the Chevrolet S-10 truck. It's a PVDF-based pressure-sensitive dry paint film called Avcoat. The product provides a high-gloss black accent color. According to Avery Dennison, auto makers have had trouble obtaining a similar high-gloss appearance with the newer, environmentally "friendly" powder coatings.

According to product manager Diana Mercier, this product differs from Avloy in that the paint film is applied manually to the plastic part, rather than in the mold. Fixturing devices can be used to secure the part while the installer manually presses the film into place, reducing the occurrence of defects.

There are two versions of this product: Avcoat pressure-sensitive thin film with a strippable carrier web and Avcoat PF, an adhesive-backed, rigid preform. Both are designed to be cost-effective alternatives to conventional painting. Avcoat's chemical resistance, weatherability, and gloss are said to exceed those of paints. Avcoat PF is offered as a less costly alternative to injection molded or stamped-metal appliques.
COPYRIGHT 1994 Gardner Publications, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1994, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Author:Sherman, Lilli Manolis
Publication:Plastics Technology
Date:Jun 1, 1994
Words:964
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